Just tried out Lakka for the first time today. Ran into these problems:
1) Lots of systems missing. It has the big ones, but little guys like NGPC and some popular projects like MAME aren't working on RPi.
2) The rom indexing is fast and offline, but it only works with No-Intro romsets.
3) No gui for Wi-Fi and Bluetooth.
4) N64 runs incredibly slow. Slower than Mupen64 run on its own.
The biggest problem is that RPi support isn't the goal for the project. They're aiming for much more powerful systems that can run the whole libretro gamut.
The big advantage is that it is very quick to get up and running. Copy roms over SMB (or put the SD card in your computer if you run linux) hook up a controller and you are ready to play.
I'd still stick with Emulationstation based distros with Retroarch on the backend. Lakka will beat them out one day, but probably not on the RPi.